A Virtual Router Redundancy Protocol (VRRP) is a protocol to make a node redundant in a network. In the VRRP, one of the nodes that belong to a specific VRRP group is handled as a master node and the rest of the nodes are handled as backup nodes. Normally, only the master node performs processing, and one of the backup nodes performs the processing instead when a failure occurs in the master node.
A virtual media access control address (MAC address) and a virtual Internet Protocol address (IP address) are assigned to each VRRP group. In a network using the VRRP, switches and the like are configured in the network such that data addressed to the virtual MAC address and the virtual IP address is transferred to the master node.
The VRRP is also used to make a virtual router redundant. For example, two virtual routers belonging to the same VRRP group are caused to operate on separate physical servers, and one of the virtual routers is handled as a master node and the other as a backup node. When a failure occurs in the physical server in such a situation, communication through the virtual routers is difficult to perform unless switching between the master node and the backup node is properly performed. Technologies in related art do not focus attention on such a problem. Related art documents include Japanese Laid-open Patent Publication No. 2003-51835.